1. Field of the Invention
The present invention provides a microstrip antenna transceiver which is capable of switching polarizations.
2. Description of the Prior Art
Satellite communication has advantages of huge coverage and no interference caused by ground environments, and is widely used in military applications, detection and commercial communications services such as satellite navigation, a satellite voice broadcast system or a satellite television broadcast system. Nowadays, many electronic devices, such as smart phones, tablet personal computers, and so on can receive satellite signals via an external antenna. In general, the frequency of satellite signals ranges from 1.466 GHz to 1.472 GHz and two orthogonal signals are provided within the band at the same time, wherein one of the orthogonal signals is a left-handed polarized signal and the other is a right-handed polarized signal. Therefore, a left-handed polarized antenna module and a right-handed polarized antenna module are required to receive the two orthogonal signals. However, practically, an electronic device does not handle the two orthogonal signals at the same time and only selects one. Moreover, two independent antenna modules occupy much space and increase the cost, so the left-handed polarized antenna module and the right-handed polarized antenna module are preferably combined to one antenna module.
A conventional antenna transceiver comprises two switch elements, a hybrid circuit and a patch antenna. The hybrid circuit comprises two input transmission ports and two output transmission ports. When the two switch elements are not conducted simultaneously (i.e., only one switch element is turned on at a time) and control a signal received to enter the hybrid circuit via only one of the input transmission ports, the hybrid circuit equally partitions the signal into two transmission signals with a phase difference of 90 degrees, and then transmits the two transmission signals to the patch antenna through the two output transmission ports, respectively. Then, the patch antenna generates a vertically polarized signal and a horizontally polarized signal and radiates the vertically polarized signal and the horizontally polarized signal to the air. Since the phases of the two transmission signals have a 90-degree phase difference, a left-handed polarized antenna pattern or a right-handed polarized antenna pattern can be formed. Two feed-in points of the patch antenna are connected to two output transmission ports respectively; therefore, vertically polarized and horizontally polarized electromagnetic fields are generated after the two transmission signals equally partitioned from the signal enter the patch antenna. Besides, since the patch antenna is vertically and horizontally symmetric, energy of the vertically polarized signal and the horizontally polarized signal are not mutually affected.
As seen above, the conventional antenna transceiver has high isolation for two orthogonal signals. However, the length and width of the hybrid circuit need to be ¼ wavelength in order to perform the hybrid circuit, so that the hybrid circuit requires large plate area and the cost is increased for the present satellite signals of low frequency. Therefore, how to reduce the cost of the antenna and handle the two orthogonal signals at the same time becomes a goal in the industry.